Environmental Engineering Reference
In-Depth Information
The reduction of nitrate could also occur in a different pathway producing nitrite and nitrogen
gas. The reactions involved are shown in Reactions 37.3 through 37.6 [65]:
0
−
+
2
+
+
4
Fe
+
NO
+ →+
10
HFe
4
NHH
+
3
2
O
()
(3 7. 2)
()
s
3
()
aq
(aq)
()
aq
4
()
aq
0
−
+
2
+
5
Fe
+
2
NO
+ →+
12
HFe
5
NHO
+
l)
(3 7. 3)
()
s
3
()
aq
(aq)
()
aq
2
()
q
2
(
0
−
+
2
+
−
Fe
+
NO
+ →+
2
HFe
OHO
+
)
(3 7. 4)
()
s
3
()
aq
(aq)
()
aq
2(aq)
2
(
l
0
2
+
−
2Fe
+
2
HOO
+ →+
2
Fe
4
OH
(3 7. 5 )
()
s
2
( l)
2
()
aq
()
aq
(aq)
0
2
+
−
Fe
+ →+
2
HO
Fe
H
+
2
H
(3 7. 6 )
()
s
2
( l)
()
aq
2
()
g
()
aq
In slightly basic to neutral pH in the leachate, nitrate reduction through nitrite could be
more favorable. Although the nitrite-N concentration in the tested leachate sample was
very low, it increased over time with the reduction of nitrate by S-NZVI. This is in agree-
ment with the literature [65,66].
The ammonium concentrations should also be considered for a better understanding of
the process (Figure 37.7c). In anoxic conditions, ammonium can be converted to nitrogen
gas, whereas nitrite is the electron acceptor [46]. However, in this experiment, we observed
formation as well as decline of the ammonium concentrations. H
2
formed as in Reaction
37.6 could be used by denitrifying bacteria/denitriiers such as
Micrococcus
,
Bacillus
, and
Pseudomonas
to convert nitrate to nitrogen gas or nitrous oxide [46].
37.3.4 Phosphate
PO
3
( )
Removal by Nanomaterials
According to the results from the batch experiment, GNP showed the highest phosphate
removal density compared with the other sorbents. Phosphate removal has reached the
equilibrium within the irst 12 h for S-NZVI, indicating 7.484 × 10
−7
mol/m
2
removal den-
sity (Figure 37.7d). The second best material for phosphate removal was S-NZVI, which
indicated 8.0 × 10
−6
mol/m
2
after 120 h. This may be due to the coagulation effect of GNP.
Except AgNP, other sorbent materials (IONP and NZVI) showed 70% phosphate removal
density during the study period. The phosphate has a strong tendency to be adsorbed
on metal surfaces, through surface OH bonds, and precipitated with iron species [67,68].
During the corrosive leaching of the Fe(III) ion, the pure metal phosphates are precipi-
tated in the intermediate at high pH range. At lower pH, phosphate could be adsorbed onto
iron hydroxides, oxyhydroxides, and mixed valence green rust. Furthermore, phosphate
removal can also increase through a biological phosphate removal process since the anoxic
environment is favorable for the microorganism (
Microlunatus phosphovorus
,
Lampropedia
spp., etc.) activity that contributed to degrade phosphate [69].
37.3.5 BOD Removal by Nanomaterials
Figure 37.8 shows the BOD values of control and nanomaterial-treated leachate samples
with time. The control sample and nanoparticle-treated sample, except S-NZVI, showed
